In eukaryotes the genetic factors involved in the regulation of gene expression are not well understood. We propose to investigate Beta-glucuronidase in Drosophila as a model for the genetic analysis of such regulation. The proposed studies are similar to those initiated in mice and should allow us to dissect the processes concerned with the final expression of enzyme activity. Such processes include the rate of synthesis, time of appearance, intracellular licalization, nature and extent of post-translational modifications, and rate of degradation. Our initial studies will concentrate on the identification and biochemical characterization of an array of natural variants for Beta-glucuronidase activity. Other work will be directed towards the production of antisera specific for Beta-glucuronidase. Such antisera will serve as a means of distinguishing two possible classes of activity variants.